DESCRIPTION: (Provided by the Applicant) In HIV infected individuals, HSV infections increase in frequency and severity as CD4 T cells counts wane. This application proposes a novel strategy to control HSV-1 infection by improving the effectiveness of antibody and complement (C) in host defense. HSV-1 uses stealth strategies to evade antibody and C attack. HSV-1 glycoprotein gC interferes with C activation at several steps in the C cascade, rendering C ineffective against the virus. However, if a critical gC domain that binds C3 is deleted from the virus, C reduces HSV-1 virulence 50- to 100-fold. HSV-1 glycoprotein gE evades antibody by binding the IgG Fc domain and blocking Fc-mediated activities, including C activation and antibody-dependent cellular cytotoxicity. An HSV-1 gE mutant virus unable to bind the IgG Fc domain is 50 to 100-fold less virulent than wild-type virus because of enhanced antibody effectiveness. The applicants constructed a mutant virus altered in both gC and gE and demonstrate that these glycoproteins act in synergy to evade antibody and C attack, since the gC-gE double mutant virus is 1,000- to 10,000-fold less virulent than wild-type virus. As part of the CFAR initiative at Penn, an HIV patient registry and specimen repository was developed in 1999 to enroll subjects cared for at Penn clinics. The applicants will analyze serum samples obtained from the repository to determine whether HIV subjects maintain adequate levels of HSV antibodies and C to neutralize a mutant HSV-1 strain that is defective in gC and gE immune evasion. They postulate that the majority of HIV/HSV-1 co-infected subjects will maintain sufficient antibody and C titers to neutralize at least 100-fold more gC-gE mutant than wild-type virus. Based on preliminary results, they postulate that antibodies produced during natural HSV-1 infection cannot prevent gC and gE immune evasion because the domains involved are "hidden" from the host. Therefore, they propose to modify gC and gE immune evasion domains to improve immunogencity. They will test these altered proteins as vaccine candidates in murine models to determine whether the antibodies produced block gC and gE immune evasion and reduce disease severity. CD4-knockout mice will be used to investigate whether antibody and C can compensate for waning CD4 T cell immunity if virus is defective in immune evasion. Preventing viral stealth may greatly improve antibody and C activities in HIV subjects, and may offer a novel strategy for developing HSV and other viral vaccines.